Body area networks (BAN) are a low-power short-range wireless technology that can be used for medical applications, such as digital band-aids and pacemakers, and for entertainment and consumer electronics applications, including heads-up displays and wireless gaming. Body area networks are being designed for use in several radio frequency bands, including 400 MHz Medical Implant Communications Service (“MICS”) band, 900 MHz and 2.4 GHz Industrial, Scientific and Medical (“ISM”) band, and 3.1-10.6 GHz Ultra Wideband (UWB) band.
A symbol is a representation of a bit value, either 0 or 1, often used in wireless communications. The particular value represented by a symbol may be determined based on when a signal is transmitted by a device and when that signal energy is received by a device that is listening for signals. Symbols may be modulated, or made to appear to a receiving device as a 0 or a 1, in a multitude of ways. A transceiver, or a device capable of transmitting and receiving symbols, must agree with another transceiver on a modulation scheme in order for the two devices to communicate. In some modulation schemes, a symbol may be thought of as positions in which a signal may be transmitted. In these “pulse position modulation” schemes, transmission of a signal in one position may represent a ‘0’ bit, whereas transmission in another position may represent a ‘1’ bit.
A refinement of this scheme is to use multiple burst positions, as opposed to a single pulse position, to represent a bit. This scheme is called “burst position modulation.” The multiple burst positions that replace a single pulse position represent a single bit value, and the receipt of signal energy in any of the multiple burst positions for a particular bit is interpreted as a transmission of that particular bit value. The burst position in which a signal is transmitted to represent a particular bit value may change from symbol to symbol. Changing, or hopping, the burst position from one symbol to the next in a deterministic way is called time-hopping. The hopping pattern is known to both the transmitter and the receiver. Such time-hopping mitigates interference from neighboring devices and serves to make the transmitted signal more random, which results in a flat spectrum (i.e., no spectral lines).